It is known in the art to which this invention pertain to produce corrugated thermoplastic tubing or tile for drainage and water flow systems utilizing forming apparatus commonly termed a corrugator. Exemplary apparatus for this purpose generally comprises a pair of complementary upper and lower mold assemblies, each comprising an endless chain of articulately interconnected mold blocks, and means for guiding the mold blocks along an endless track having a forward run and a return run. Each mold block is complementary to a respective mold block of the other assembly, and the mold blocks cooperate in pairs along the forward run to form an axially extending tunnel defining a tubular mold having a corrugated wall. The mold assemblies are positioned so as to locate the extrusion head at the entrance to the tunnel coaxially therewith, and extruded thermoplastic material is expanded by blow molding to conform to the interior surface of the mold. In such an arrangement, it is also conventional to cool the mold blocks in order to augment the formation of the thermoplastic tubing, and to induce a vacuum between the extruded plastic and the wall of the molding tunnel to assure the mating thereof. U.S. Pat. No. 3,981,663 issued Sept. 21, 1976 is generally illustrative of a corrugator of the foregoing character.
Rotary travel of the mold blocks necessarily requires complex structures and entails inconvenience in effecting the coolant and vacuum connections, since positive mold cooling occurs only during the return run of the mold blocks along the continuous irreversible rotary or generally helical path. Rather cumbersome rotary type hose disconnects is one pursuit known to the art to alleviate this problem.
Complete stoppage of the corrugator is also required in order to effect mold changes. To explain, in addition to prescribed lengths of the corrugated flexible plastic tubing or tile, requirements exist for tubing fittings exemplified by couplings, adapters, end caps, and the like. Production of such fittings requires mold changes on the corrugator, and consequent down time of the entire apparatus. This fact is noted near the end of the specification in U.S. Pat. No. 4,439,130 issued Mar. 27, 1984.
This same patent in Column 9 thereof also notes that the mold assemblies not dedicated to the formation of the molding tunnel are continuously returned along the return trackway where they are cooled. Quite clearly, the provision of a greater number of mold assemblies than that actually required for production substantially increases tooling cost, and other disadvantages naturally flow therefrom.